Oxygen consumption and ventilation during constant-load exercise in runners and cyclists

The effect of using specialized or no specialized muscle groups on ventilatory threshold (VT) and on maintenance of steady-state oxygen consumption during long term exercise on treadmill and on cycle ergometer was studied in ten endurance runners and nine cyclists. Initially, maximum oxygen consumption (VO2max) and VT were determined. Oxygen consumption (VO2) ventilation (VE) respiratory rate (f), and blood lactate (in the beginning and at the end of exercise) were measured during exercise at constant relative loads of 60, 70, and 80% of VO2max. In the runners, both VO2max and VT (expressed as % VO2max and VO2 l/min) were greater on treadmill than on cycle ergometer and in the cyclists, VO2max was higher on cycle ergometer than on treadmill, but no differences in VT were detected between the two tests. The VO2, VE, and f drifts correlated with blood lactate level as well as with the calculated VT. The results suggest that the effect of using specialized or no specialized muscle groups on the maintenance of VO2 steadiness is achieved through training-induced changes on the level of blood lactate and, in VT.     

Acute alcohol consumption aggravates the decline in muscle performance following strenuous eccentric exercise

This study investigated the effects of acute moderate alcohol intake on muscular performance during recovery from eccentric exercise-induced muscle damage. Eleven healthy males performed 300 maximal eccentric contractions of the quadriceps muscles of one leg on an isokinetic dynamometer. They then consumed a beverage containing 1 g/kg bodyweight ethanol (as vodka and orange juice) (ALC). On another occasion they performed an equivalent bout of eccentric exercise on the contralateral leg after which they consumed an isocaloric quantity of orange juice (OJ). Measurement of maximal isokinetic (concentric and eccentric) and isometric torque produced across the knee, plasma creatine kinase (CK) concentrations and muscle soreness were made before and at 36 and 60 h following each exercise bout. All measures of muscle performance were significantly reduced at 36 and 60 h post-exercise compared to pre-exercise measures (all p < 0.05). The greatest decreases in peak strength were observed at 36 h with losses of 12%, 28% and 19% occurring for OJ isometric, concentric, and eccentric contractions, respectively. However, peak strength loss was significantly greater in ALC with the same performance measures decreasing by 34%, 40% and 34%, respectively. Post-exercise plasma creatine kinase activity and ratings of muscle soreness were not different between conditions (both p > 0.05). These results indicate that consumption of even moderate amounts of alcohol following eccentric-based exercise magnifies the normally observed losses in dynamic and static strength. Therefore, to minimise exercise related losses in muscle function and expedite recovery, participants in sports involving eccentric muscle work should avoid alcohol-containing beverages in the post-event period.     

Shortened T2 after exercise in ischemic skeletal muscle

PURPOSE: To detect skeletal muscle ischemia with transverse relaxometry after ischemic exercise. MATERIALS AND METHODS: Ten subjects with intermittent claudication were studied. T2 was measured in the gastrocnemius and soleus muscles (m. gastrocnemius and m. soleus) at rest and repeatedly after exercise during 45 minutes of recovery. Prior to MRI a symptom-limited treadmill exercise was performed, and the ankle-arm blood pressure index (AAI) was measured at rest and after exercise. RESULTS: In the 14 legs with ischemic pain, a diverging response was found in the calf: T2 increased in m. gastrocnemius by 5.6% +/- 4.9%, but decreased in m. soleus by -1.2% +/- 4.4% (P < 0.001). Moreover, 13 regions in legs with ischemic pain and reduced AAI (from 0.7 +/- 0.2 at rest to 0.31 +/- 0.15 after exercise) had shortened T2 (-3.6% +/- 1.8%) immediately after exercise. This finding was most frequent in m. soleus and two regions of m. gastrocnemius. Recovery was delayed in the latter two regions. CONCLUSION: T2 may identify ischemic muscles after hypoxic exercise. Shortened T2 suggests a reduced water content (e.g., distribution volume of water) and may affect the upslope kinetics of an extravascular perfusion tracer. The different responses to ischemia by the soleus and gastrocnemius muscle may be due in part to their different fiber type compositions.     

Postexercise oxygen consumption and substrate use after resistance exercise in women

OBJECTIVE: This study investigated the acute effects of 45 min of resistance exercise (RE) on excess postexercise oxygen consumption (EPOC) and substrate oxidation 120 min after exercise in moderately trained women. METHODS: Ten RE trained women (age = 29 +/- 3 yr; ht = 168 +/- 8.3 cm; wt = 59 +/- 5.7 kg; VO2max = 38.3 +/- 4.7 mL.kg-1.min-1) underwent two trials: control sitting and RE. Subjects acted as their own controls in a random counterbalanced design. A 2-d nonexercise period was established between testing trials. Oxygen consumption (VO2) and respiratory exchange ratio (RER) were measured continuously by indirect calorimetry before, during, and after exercise and on a separate control day. RE consisted of 3 sets of 10 exercises at 10-repetition maximum with a 1-min rest period between each set. Fingertip samples of blood lactate concentration [BL] were collected immediately postexercise and every 30 min thereafter until [BL] returned to resting baseline values after exercise. RESULTS: The overall 2-h EPOC was 6.2-L (RE = 33.4 +/- 5.1 L vs control = 27.2 +/- 0.3 L), corresponding to an 18.6% elevation over the control period. RER was significantly (P < 0.01) below the control RER from minute 30 to minute 120 postexercise (RE = 0.75 +/- 0.01 vs control = 0.85 +/- 0.01). During the last 30 min of recovery, VO2 and [BL] had returned to control/baseline values and fat oxidation was significantly (P < 0.0001) higher (29.2 vs 16.3 kcal) after RE compared with the control trial. CONCLUSION: These data indicate that in young RE trained women, acute RE produces a modest increase in VO2 during a 2-h recovery period and an increase in fat oxidation.     

Oxygen consumption, lactate accumulation, and sympathetic response during prolonged exercise under hypoxia

Six men (33 +/- 3 years old) performed 1 h ergocycle exercise (60% VO2 max) at sea level and at a simulated altitude of 3000 m. A similar relative exercise intensity corresponded to a lower absolute work load (139 +/- 4 W) in hypoxic than normoxic (163 +/- 4 W) conditions. Lower oxygen uptake (VO2) with no change in ventilation (VE), respiratory exchange ratio (R), and heart rate (Hr) were observed during exercise under hypoxia compared to normoxia. A slow rise in VO2, after the initial 5 min exercise, was observed in normoxic (+ 230 ml/min) as well as in hypoxic (250 ml/min) conditions that might be, in part, related to oxidative removal of blood lactate. Peak blood lactate concentration reached at 30 min of exercise was similar in normoxia (4.5 +/- 0.4) and in hypoxia (4.7 +/- 0.5). However, while the lactate level decreased during exercise at sea level, it remained elevated throughout exercise in altitude. Blood lactate concentration measured at the end of exercise was significantly (P less than 0.05) higher in hypoxic (4.4 +/- 0.3) than in normoxic (3.2 +/- 0.4) conditions. Catecholamine response to exercise was similar in both conditions. We conclude that during prolonged exercise at a given relative work load, hypoxia does not affect cardiorespiratory and sympathetic responses but tends to increase blood lactate accumulation. Higher blood lactate concentrations during hypoxic exercise seems to reflect alterations in the removal of blood lactate rather than changes in glycolytic flux.     

Creatine kinase and muscle soreness after repeated isometric exercise

This study examined adaptation to isometric exercise with regard to changes in serum creatine kinase (CK) activity and muscle soreness. Forty-five college-age males were placed into six groups, each performing two bouts of strenuous isometric exercise of the knee extensors. In experiment 1 (N = 27), after performing the first bout of exercise, groups A, B, and C performed the second bout 3, 6, and 9 wk later, respectively. In experiment 2 (N = 18), groups D, E, and F performed the second exercise bout 1, 2, and 3 wk after the first bout, respectively. In experiment 3, group D performed two additional exercise bouts; thus, this group performed a total of four bouts spaced 1 wk apart. Muscle soreness and CK were assessed prior to and 6, 18, and 24 (or 42) h following each exercise. In experiment 1, no significant difference in soreness or serum CK was found between bouts 1 and 2. In experiment 2, a significant decrease in the CK and soreness responses was found on bout 2 compared with bout 1 (P less than 0.05). In experiment 3, serum CK and soreness responses were highest following bout 1 while bouts 2, 3, and 4 were not significantly different from one another. Performance of this isometric exercise results in an adaptation that lasts approximately 3 wk, with the greatest adaptation occurring after one bout.     

Oxygen consumption during photodynamic therapy in vitro

The consumption of dissolved molecular oxygen was measured during photodynamic therapy in vitro. Aqueous solutions of hematoporphyrin derivative (HpD) containing different concentrations of serum or numbers of cells were prepared. Decrease in oxygen in the solution and cell suspensions was monitored during light-irradiation (at a wavelength of 610 to 640 nm). The rate of oxygen consumption increased with increasing concentrations of HpD, serum levels or numbers of cells. Upon repeated irradiation of the same solutions (after restitution of the initial pO2 of 100 mm Hg), the rate of oxygen consumption decreased indicating a disaggregation process of HpD. The rate of oxygen content of the solutions decreased independently of the actual oxygen partial pressure. Even at a low pO2 below 10 mm Hg, oxygen consumption was unimpeded until the solutions were free of oxygen. No O2-consumption was noted in aqueous solutions of HpD (up to 40 g/ml) without serum or cells during irradiation.     

Intramuscular pressures and muscle metabolism after short-term and long-term exercise

Intramuscular pressures were measured in the anterior tibial and deep posterior muscle compartments in eight healthy individuals before, during, and after short-term exercise and in 38 individuals after long-term exercise by the wick catheter method. Muscle biopsies were also taken and analyzed for muscle fiber distribution, water content, and lactate content. There were no elevations of the intramuscular pressures in the anterior tibial and the deep posterior muscle compartments after exercise nor was there any evidence of edema or anaerobic metabolism in the muscles examined.     

Oxygen uptake in one-legged and two-legged exercise

PURPOSE: The purpose of this study was to determine the primary factors causing the differential oxygen uptake (VO2) response at submaximal intensities between one-legged and two-legged exercise, and whether peak oxygen uptake (VO2peak) increases in proportion to the increase in active muscle mass. METHODS: Two different types of exercise were used for this experiment, each requiring a different movement, a different method of stabilizing posture, and, finally, a different limiting VO2peak. In experiment 1, nine male subjects performed one-legged cycling (OLC) and two-legged cycling exercise (TLC) at a pedaling rate of 80 rpm. The exercise intensity was first set at 80 W and was increased by 40 W every 3 min until exhaustion. In experiment 2, six healthy male subjects performed one-legged knee-extension (OKE) and two-legged knee-extension (TKE) exercise at a rate of 50 contractions per minute. The knee-extension exercise was done at constant work rates for a 3-min session in OKE or a 4-min session in TKE. The exercise bouts were performed intermittently at four to seven different submaximal intensities and VO2 was determined at each intensity in all exercises. RESULTS: At submaximal intensities, VO2 in relation to work rate of one-legged exercise was more steep than those of two-legged exercise, and the mean values of VO2 were significantly higher in one-legged exercise than those in two-legged exercise in both knee extension and cycling exercise. Mean values of VO2peak for two-legged exercise were significantly higher than that for one-legged exercise (P < 0.01); however, it was much lower than two times of that for one-legged exercise even in knee extension exercise where the VO2peak would be limited peripherally. CONCLUSION: The findings of this study suggest that the differential VO2 response between one-legged and two-legged exercise would be attributed not only to the difference in force application throughout the exercise movement and to the effect of a postural component but also to the inhibited circulatory response caused by the multiple limb exercise. In addition, it was supposed that VO2peak does not increase in proportion to the exercising muscle mass even during smaller muscle activity where the cardiac pumping capacity has not reached its upper limit.     

Oxygen consumption during functional electrical stimulation-assisted exercise in persons with spinal cord injury: implications for fitness and health

A lesion in the spinal cord leads in most cases to a significant reduction in active muscle mass, whereby the paralysed muscles cannot contribute to oxygen consumption (V O(2)) during exercise. Consequently, persons with spinal cord injury (SCI) can only achieve high V O(2) values by excessively stressing the upper body musculature, which might increase the risk of musculoskeletal overuse injury. Alternatively, the muscle mass involved may be increased by using functional electrical stimulation (FES). FES-assisted cycling, FES-cycling combined with arm cranking (FES-hybrid exercise) and FES-rowing have all been suggested as candidates for cardiovascular training in SCI. In this article, we review the levels of V O(2) (peak [V O(2peak)] and sub-peak [V O(2sub-peak)]) that have been reported for SCI subjects using these FES exercise modalities. A systematic literature search in MEDLINE, EMBASE, AMED, CINAHL, SportDiscus and the authors' own files revealed 35 studies that reported on 499 observations of V O(2) levels achieved during FES-exercise in SCI. The results show that V O(2peak) during FES-rowing (1.98 L/min, n = 17; 24.1 mL/kg/min, n = 11) and FES-hybrid exercise (1.78 L/min, n = 67; 26.5 mL/kg/min, n = 35) is considerably higher than during FES-cycling (1.05 L/min, n = 264; 14.3 mL/kg/min, n = 171). V O(2sub-peak) values during FES-hybrid exercise were higher than during FES-cycling. FES-exercise training can produce large increases in V O(2peak); the included studies report average increases of +11% after FES-rowing training, +12% after FES-hybrid exercise training and +28% after FES-cycling training. This review shows that V O(2) during FES-rowing or FES-hybrid exercise is considerably higher than during FES-cycling. These observations are confirmed by a limited number of direct comparisons; larger studies to test the differences in effectiveness of the various types of FES-exercise as cardiovascular exercise are needed. The results to date suggest that FES-rowing and FES-hybrid are more suited for high-intensity, high-volume exercise training than FES-cycling. In able-bodied people, such exercise programmes have shown to result in superior health and fitness benefits. Future research should examine whether similar high-intensity and high-volume exercise programmes also give persons with SCI superior fitness and health benefits. This kind of research is very timely given the high incidence of physical inactivity-related health conditions in the aging SCI population.     

Oxygen consumption and muscle fatigue induced by whole-body electromyostimulation compared to equal-duration body weight circuit training

Background

Whole-body electromyostimulation (WB-EMS) has become increasingly popular under the promise to offer a time-saving and effective exercise protocols. Few studies estimating the training intervention intensity of WB-EMS are available in the literature.

Aim

The aim of this study was first to estimate the metabolic demand and muscle fatigue induced by a training session with WB-EMS, and second to compare them to a control intervention.

Methods

Ten young participants performed two training sessions: an experimental condition constituted by five exercises with superimposed WB-EMS and a control condition constituted by five body weight exercises. Both sessions lasted 15 min and were based on isometric intermittent contraction (6 of contraction interspersed by 4 s of rest). Muscle fatigue was assessed by determining the force decrease in the following tests: isometric mid-thigh pull; plyometric push-up; counter-movement jump. Oxygen consumption and energy expenditure were recorded by measuring respiratory gases exchange to quantify the metabolic demand of the exercises.

Results

The WB-EMS intervention required greater volume of oxygen consumed (WB-EMS 1584 ± 251 ml/min; control 1465 ± 216 ml/min, p = 0.006) and energy expenditure (WB-EMS 470 ± 71 kcal/h; control 438 ± 61 kcal/h, p = 0.013) than in control intervention. Overall, the WB-EMS training induced muscle fatigue (all PRE vs POST tests p ≤ 0.02) whereas the body weight exercises did not (all p > 0.14).

Conclusions

These results indicate that WB-EMS intervention constituted a vigorous physical activity. The WB-EMS required also a greater metabolic demand and greater muscle fatigue than a traditional body weight circuit training. Thus, WB-EMS can be considered as an alternative training tool for physically active individuals.

     

Ibuprofen and acetaminophen: effect on muscle inflammation after eccentric exercise

PURPOSE: We examined the influence of ibuprofen and acetaminophen on muscle neutrophil and macrophage concentrations after novel eccentric contractions. METHODS: Twenty-four males (25 +/- 3 yr) were divided into three groups that received the maximal over-the-counter dose of either ibuprofen (1200 mg x d-1), acetaminophen (4000 mg x d-1), or a placebo after eccentric contractions of the knee extensors. Biopsies from the vastus lateralis were taken before and 24 h after exercise. Inflammatory cells were quantified in muscle cross-sections using immunohistochemistry. RESULTS: Macrophage concentrations were elevated by 1.5- to 2.5-fold (P < 0.05) at 24 h postexercise relative to preexercise concentrations, whereas neutrophil concentrations were not significantly elevated. Muscle inflammatory cell concentrations were unaffected by treatment with ibuprofen or acetaminophen when compared with placebo. CONCLUSIONS: Maximal over-the-counter doses of ibuprofen or acetaminophen, when administered therapeutically, do not affect muscle concentrations of neutrophils or macrophages 24 h after a novel bout of eccentric contractions.     

Oxygen uptake kinetics during exercise.

The characteristics of oxygen uptake (VO2) kinetics differ with exercise intensity. When exercise is performed at a given work rate which is below lactate threshold (LT), VO2 increases exponentially to a steady-state level. Neither the slope of the increase in VO2 with respect to work rate nor the time constant of VO2 responses has been found to be a function of work rate within this domain, indicating a linear dynamic relationship between the VO2 and the work rate. However, some factors, such as physical training, age and pathological conditions can alter the VO2 kinetic responses at the onset of exercise. Regarding the control mechanism for exercise VO2 kinetics, 2 opposing hypotheses have been proposed. One of them suggests that the rate of the increase in VO2 at the onset of exercise is limited by the capacity of oxygen delivery to active muscle. The other suggests that the ability of the oxygen utilisation in exercising muscle acts as the rate-limiting step. This issue is still being debated. When exercise is performed at a work rate above LT, the VO2 kinetics become more complex. An additional component is developed after a few minutes of exercise. The slow component either delays the attainment of the steady-state VO2 or drives the VO2 to the maximum level, depending on exercise intensity. The magnitude of this slow component also depends on the duration of the exercise. The possible causes for the slow component of VO2 during heavy exercise include: (i) increases in blood lactate levels; (ii) increases in plasma epinephrine (adrenaline) levels; (iii) increased ventilatory work; (iv) elevation of body temperature; and (v) recruitment of type IIb fibres. Since 86% of the VO2 slow component is attributed to the exercising limbs, the major contributor is likely within the exercising muscle itself. During high intensity exercise an increase in the recruitment of low-efficiency type IIb fibres (the fibres involved in the slow component) can cause an increase in the oxygen cost of exercise. A change in the pattern of motor unit recruitment, and thus less activation of type IIb fibres, may also account for a large part of the reduction in the slow component of VO2 observed after physical training.